Geometric Nonlinear Analysis Of Long-Span Steel Box Girder Cable-Stayed Bridge

The cable-stayed bridge is playing a increasingly important role in modern bridge area, and so far its span length has pasted more than 1000 meters. It's cannot be ignored the problem of geometric nonlinearity because of the increasing span. This paper is concerning about the geometric nonlinearity of the cable-stayed bridge.First, this dissertation introduces the history and developing of cable-stayed bridge, and describes the research status of the theory of geometric nonlinearity for cable stayed bridge.Second, this thesis introduces three calculating formulations, such as the UL formulation, TL formulation and CR formulation, and its application. Three geometrical nonlinearity factors for cable stayed bridge are explained, that are the large displacement, cable-sage effects and combined effects of bending moment and axial force. Also the problem of the solution and convergence of the non-linear equations are talked about.At last, taking the Xiangshangang bridge whose span is 688m as research background, the paper mainly studies the cable force optimization under linearity and geometric nonlinearity of the finite element model. And analysis of the linearity and geometric nonlinearity during the construction stage and a finished bridge state are made respectively. According to the comparison between those results of computation, conclusions are obtained as following:(1)In the three factors of geometric nonlinearity, cable sag effect has the most obvious effect on the moment of main girder and nonlinear of large displacement has greater effect, while the combined effect of moment and axial force has the least influence. Further, the effect degree is different in different construction phase.(2)Under dead load the cable sag effects is the main point of nonlinear behaviors of cable-stayed bridge, and the combined effects of bending moment and axial force and the large displacement are relatively little. So it is not enough if we only execute linear analysis to a cable-stayed bridge.(3) It tends to be not safe when calculating the live load effect on long span cable-stayed bridge in a linear way, compared with the nonlinear results, the difference can reach 10%.so the geometric nonlinearity should be considered.